Internal combustion engines, especially compression ignition engines such as diesel engines, utilize EGR to reduce emissions. An EGR system typically includes a flow circuit between the engine exhaust system and the engine intake system with an EGR cooler and an EGR valve within the flow circuit. EGR coolers are heat exchangers that typically use engine coolant to cool exhaust gas being recirculated into the intake system of the engine. Engine exhaust gas typically includes combustion by-products, such as unburned fuel, many types of hydrocarbon compounds, sulfur compounds, water, and so forth.
Various compounds may condense and deposit on interior surfaces of engine components when exhaust gas is cooled. The EGR cooler and the EGR valve are prone to condensation of compounds in the exhaust gas passing through it. The condensation is especially evident during cold ambient conditions, low exhaust gas temperatures, and/or low exhaust gas flow rates through the EGR cooler such as during idling. In some systems, in order to mitigate fouling of the EGR system components, the EGR valve is commanded to close by the Engine Control Unit (ECU) after sensing extended engine idling.
Condensation inside the EGR cooler, or fouling, decreases the percent-effectiveness of the EGR cooler. EGR coolers are designed to cope with condensation of hydrocarbons by incorporating anti-fouling features, such as appropriate geometries that inhibit excessive accumulation of condensates and a designed-in extra capacity that is intended to be lost to fouling during service of the cooler.
The incorporation of anti-fouling features, and the increased size of EGR coolers make cooler design complicated and costly. Accordingly, the present inventors have recognized that there is a need for an EGR system having an EGR cooler that is able to maintain higher efficiency without requiring complicated anti-fouling mechanisms or an increased cooler size.
The present inventors have recognized that there is a need to provide an EGR system with reduced fouling due to hydrocarbon condensation at low exhaust manifold gas temperatures.